Adhesives



Patented Dec. 1, 1942 ADHESIVES Paul B. Davidson, Wilkinsburg, Pa., andJulius R.

Adams, Westiield, Mass, a'ssignors to old 001- l ony Envelope Company,Westfleld, Mass, a corporation of Massachusetts No Drawing; ApplicationMarch 17, ran.

Serial No. 383,792

4 Claims. (c1. 106-210) This invention relates to improvements inadhesives and is more particularly related tosocalled gums for use inconnection with envelopes or otherdevices where it is desired toadhesively secure .ftogether. adJacently-disposed surfaces, especiallv.paper surfaces 7 as in the case of envelopes v 1 ThIs'appIication is acontinuation in part of an application Ser. No. 202,882 filed by us onApril 19, 1938, issued as Patent No. 2,241,700.

It is a principal objector the invention to provide an.,adhesive for usewith paper-which is so constructed chemically that it will not discoloror, otherwise deteriorate with age. That is to say. we have conceived anadhesive which will not have the tendency to discolor regardless ofclimate'or other conditions under which the envelopes or other articlesare stored.

It has always heretofore been a serious difiiculty in the envelopeindustry that the envelopes, after storage on shelves or the like, willbecome discolored due to reaction between the gum or adhesive andelements in the paper. It appears that the cause of discoloration is theformation of colored or humus-like substances due toreac tion betweendegraded protein which is necessarily present in any ordinarily sizedpaper and the reducing sugars which are ordinary paper adhesive. 1 I

A further object of the invention is to provide an envelopeadhesivewhich has special properties andv characteristics particularly adaptingthem for use in the manufacture of envelopes. It is the usual practicein the envelope industry to apply the gumthereto by means of what iscalled an envelope machine and it will be appreciated that in order thatapplication of the gumbe carried on efilciently and economically theadpresent in any heslve mustremaln suiljlciently fluid and nonpasty foran ample length of time. The gums of this inventionnot only have thenon-discoloration properties above-mentioned but also they are properlyfluid for use in the envelope machine. V v y After considerable researchwe have come to ,the conclusion that the problem of discoloration can besolved. Heretofore, to our knowledge, no one has ever even attemptedtodeal with the matter of discoloration, much less provide an adhesiveadapted to eliminate it. Noris there any prior art which suggests anyprevious treatment or procedure to provide an envelope gum which is bothsuiiiciently fluid and not capable of causing discoloration.

Our invention consists f broadly in providing paper adhesives which haveas a' base a certain amount of partially-'dextrinized starch and con--tain one or more of'a group-of fluidify'ing sub stances which arecapable of both sufliciently inhibiting objectionable gel formation andpreventing'discoloration. That is to say, the composi tion is such thatit is properljfluid to permit efilclent application to the'paper by theenvelope machines andit is alsojsuch that it will not, after applicationto the paper, tend'to react with more or less degraded protein in thepaper sizingsfso as to .form' coloredfc'ompounds' which areobjectionable. I

7 After considerable.eirperiment wehave found that any gums or adhesiveswhich contain appre ciably more than 2%" by weight oflreducing' sugarsdo react unfavorably with the protein in ordinary paper, sizings soastoproduce discoloration. In other 'words, we provide an adhesivecomposition which is so---constructed chemically as to have-atotalreducingsugarcontent which is preferably not more than 2% ,byweight of the gum and we accomplish this by a combination ofpartially-dextrinized starch and .a fiuidifying agent which iscalculated toproduce the desired effect. 7 ,z

. Careful and scientifically conducted experiments' have clearly shownus that when the reducing-sugar content of1the gum doesrlse appreciablyabove: the percentage mentioned-there is, inevitably, discoloration. Forexample, a number of pieces of paper, all .the samekind, were stucktogether'with various adhesives which have been heretofore known andwith adhesives of this invention which'are aboutto be described.

as These pieces were aged by anaccelerated ageing test which had beenstandardized against natural conditions. This test consisted of placingthe pieces in testtubes, sealing, them, and

placing the .tubes in anxoven regulatedto C. I for 48 hours.

dextrins by adding cc..-of 98% ethanol, ac-

cording to the method described asthe Starch Tentative? on page 385 ofthe third edition of .Oficial andTentativeMethods of Analysis of theAssociation of Ofiicial Agricultural Chemists.

The dextrins were allowed topsettle out of as dispersion for-'48 hoursand then samples of the Association of Official Agricultural Chemistsmentioned above. It was clear from the results that the particularadhesives embodying the -features of this invention did not showdiscoloration because the reducing sugar content was below 2%, all otherthingshaving been kept equal.

We have further found thatthere are particular types of dextrin orstarch which are most suitable for accomplishing our purpose. While, asa general rule, best results can be obtained if the .reducing sugarcontent. of the 'dextrin itself before cooking is below 2%, it isnecessary that the final cooked gum contain less than 2% of reducingsugar to completely avoid discoloration. i

That is to say, the hydrolysis that takes place during the normalcooking of the gum may objectionably increase the reducing sugar contenteven though the'content oftlfie original dextrin was low. Accordingly,we preferably use a partially-dextrinized starch which is of such acomposition that when it is cooked for about thirty minutes at atemperature of around 98 C. with an approximately 40% concentratedsolution of acetic acid, it will have, upon cooling, a reducing sugarcontent of less than, or at least not appreciably more than, 2% byweight.

Another example of a preferred dextrin is one which, when cookedfor-aboutthirty minutes at a temperature of about 85C. with the sameacetic acid, will not have areducing sugar content of more than 2% byweight. That is to say, of all the variously dextrinized starches whichare commercially available those which have the just-referred-toqualifications are most suitable for the practice of this invention.

When using the terms dextrin or partially dextrinized starch hereafter,we meanjust such substances as above defined. We .found that while suchmixtures as just described might have the desired low reducing sugarcontent, they were not sufiiciently fluid for application by themachines so that it was incumbent upon us to fiuidify the mixtures inaway which would not increase appreciably the sugar content. As stated,the common way to fiuidify'heretofore has been to add more sugar; this,of course, increases the sugar content so that the gum would have all ofthe above-mentioned objections.-

Such-substances as wehave found to produce the desired result includethe amides of monocarboxylic acid containing from 2to 5 carbon atomsinclusive. We desire to here point out.

that we are concerned with amido compounds, such as acetamide, forexample, which are to be distinguished from the so-called. amido acidsheretofore disclosed in a United States Letters Patent #974,448 of 1910to one Supf. According to Rule 5 adopted by the nomenclature committeeof the joint congress of the British Chemical Society and the AmericanChemical Society held in 1923: The names of the groups NHz, NHR, NR2, NHor'NR should end in -ido only when they are substituents in an acidgroup, otherwise in -ino."

Other agents which we have found suitable are propianamide andbutyramide.

That is, we are here concerned with amides or salts. of acids, ascontrasted with what are now called amino acids and which in Supfs timewere referred to as "amido acids. .To put it another way, while in 1910,for example, the usual definition for an amido group was one where anNH: group replaces a hydrogen of the hydrocarbon, today such terminologyindicates the replacing the CH .of a carboxyiic acid to form an amidocompound. We are concerned with present-day amido compounds rather thanwhat was synonymous in 1910 with an amino group.

According to the preferred form of the method of this invention, waterand the partially dextrinized starch are mixed intimately. If desired, avolatile acid, such as acetic, may be introduced to aid in thehydrolysis of the starch and the mixture is then agitated so that theingredients thoroughly'blend.

I The composition is then heated'in any wellknown manner to within arange or preferably from 160 to 212 R, which temperature is preferablymaintained for from 20 to 60 minutes. The length of time during whichthe gum is cooked depending, of course, upon the size of the batch, thetemperature, the equipment used,-

and various other factors.

It is desirable that the mixture be cooked only -until hydrolysis to thedesired degree of dextrinization is complete and not for such a lengthof time that the reducing sugar content be substan-' tially increased.The fiuidifying agent may be now added but we do not wish to be limitedto any specific order in which the above ingredients may be added.

As final steps in-the process the gum is preferably chilled to about 100F., or below, after which the mixture is ready to be drawn.

While the proportions of the above ingredients may be greatly varied,very favorable results have been obtained when staying within thefollowing approximate ranges of proportions by weight:

' Per cent Water 10 to 18 Partially dextrinized starc to 62 Fluidifyingagent 3 to 10 If' acetic acid or-some other volatile acid is added,about 10 to 20% thereof-may be used- If it' is desired to includeglycerine, about 4 to 10% thereof may be used. While we have describedthe invention in great detail. and with respect to the. presentpreferred form thereof, it is not desired to be limited thereto sincemany changes and modifications may be made therein without departingfrom the spirit and scope of the invention. What it'is desired 'to claimand secure by Letters Patent of the United States is:

1. As 'a new article of manufacture, an envelope adhesive haying areducing sugar content 3. As a new article of manufacture, apaperenvelope adhesive of the character described consisting of, acertain amount of partially-dextrinized starch, water, and an amide ofmonocarboxylic acid containing from two to five carbon atoms inclusive,said starch, water, and amide being in such relative proportions thatthe total reducing sugar content of the adhesive is limited to about 2%of the weight thereof.

4. As a new article of manufacture, a paperenvelope adhesive of thecharacter described consisting of, a certain amount ofpartiallydextrinized starch, water, and an amide compound of the groupconsisting of acetamide, propianamide and butyramide, said starch, waterand compound being in such relative proportions that the total reducingsugar content of the adhesive is limited to about 2% of the weightthereof.

PAUL B. DAVIDSON. 'JULIUS R. ADAMS.

